Control system for reversible mills



Sept 10, 1940' A. F. KENYON 2,214,617

CONTROL SYSTEM FOR REVERSIBLE MILLS Filed May 22, 1957 4 ShQQtSv-Sheet l "IY u ./7/

WITNESSES:

WM j# wm INVENTOR #lanzo E Kenyon SPt 10. 1940. A. F. KENYoN 2,214,617

CONTROL SYSTEM FOR REVERSIBLE MILLS Filed uayzz, 1937 sheets-sneu 2 WITNESSES: INVENTOR MM /7/ 0f7z0 E Kenyon.

WMM W? Sept. l0, 1940. A. F. KENYON CONTROL SYSTEM FOR REVERSIBLE MILLS Filed May 22, 19374 4 '.:hoets-Sllge, 3

INVENTOR /7/0/720 F Kenyon.

WITNESSES:

T ORNEg )N A. F. KENYON CONTROL SYSTEM FOR REVERSIBLE MILLS Filed May 22, 1937 4 Shoots-Sheet 4 INVENTOR ,C7/07720 F. Kenyon.

WITNESSES: WMM

B C Ni" Patented sept-1o, 1940 l UNITED STATES PATENT OFFICE CONTROL SYSTEM Fon REVERSIBLE MILLS Pennsylvania Application May 2z, 1937, serial No. 144,142

29 Claims.

My invention relates, generally, to electric drives and control systems for rolling mills, and particularly to an electric drive and control system for a single stand reversible cold roll mill having a Winding reel on each side of the main roll stand of the type shown in my copending application filed January 3, 1934, S'erial No. '705,- 073, now Patent No. 2,084,035, issued June 15, 1937.

In the operation of such mills, the material which is being reduced by passing it through the main roll stand is fed to the reducing rolls from a reel upon which it'has been wound and upon being delivered from the rolls is rewound upon a second reel. When the strip of material is again passed through the rolls the rolls and reels are rotated in the opposite direction and the material is fed from the reel upon which it was last wound and rewound upon the reel from which it was last unwound. To obtain the best product from these mills, a predetermined tension is maintained on the material on both the entry and delivery sides of the rolls. This tension is obtainedby maintaining the necessary torque on 25 the individual reel motors.

It will be apparent that a very large speed variation in the reel motors is necessary both because of the necessity of maintaining the desired tension on the material from standstill through full speed rolling and to standstill again when the mill is stopped for reversal, and because of the difference in speed of the motors occasioned by the greater speed of delivery of material from the rolls than speed of entry due to reduction in 35 thickness of the material in passing through the rolls. Another variation in reel motor speed is caused by the building up of material on the reel as it is wound.l The effective diameter of the reel and therefore the reel speed is likewise changed as material is unwound from the reel.

In the operation of mills of this type the back tension on the material as it enters the rolls is obtained by operating the unwindlng reel motor as a braking generator and feeding the regenerated power back tothe power source. This requires a very large field excitation to generate sufficient back voltage at low reel speeds to feed power back to the power lines.

It has been found diicult to secure the extremely wide speed range required of these reel,

l is to provide an electric drive for a rolling mill which shall be simple and efiicient in operation and which may .be economically manufactured and installed.

A more specific object of my invention is to provide a means for extending the speed range of the Winding reel motors in an electric mill drive of the hereinbefore described character, considerably beyond the range obtainable by field control.

A further object of my invention is to provideI a means for extending the operating range of a reel motor when operating as a generator in an electric mill drive of the hereinbefore described character, considerably beyond the range obtainable by field control. v

Another object of my invention is to provide a simple and eiective control for the inching-operations of a reversible strip mill.

A still further object of my invention is to provide a simple and effective control for setting up and tensioning the material being'rolled in a reversible strip mill prior to each pass through the mill.

Another object of my invention is to provide a booster generator in series with the winding reel motor of a strip mill to extend its speed range beyond that obtainable with field control.

Another object of my invention is to provide a boosterl generator in series with the reel motor which is acting as a generator in providing regenerative braking for the unwinding reel in a strip mill to extend the range of operation o f the motor beyond that obtainable with field control.

Another object of my invention is to provide a booster generator in series circuit with each of the reel motors of a reversible strip mill so that the voltage applied to the winding reel motor may be greater than the'power source voltage and the voltage generated by the reel motor which is acting as a generator in providing regenerative braking for the unwindlng reel may be less than the voltage of the power source.

A further object of my invention is to provide a booster generator for each of the reel motors of a reversing strip mill and control meanswhereby each motor may be connected in circuit to be driven by its booster generator in setting up the material in the mill for the rolling operation.

Another object of my invention is to provide a booster generator for each of the reel motors of a reversing strip mill and control means for so connecting the boosters and motors in circuit as to cause the reel motors to properly tension the strip by virtue of the power furnished by the fv booster generators before starting each -pass of the strip through the mill.

Another object of my invention is to provide a booster generator for each of the reel motors of a reversible strip mill and to so control the operation of the i'nill, reel motors and boosters as to use the boosters to furnish power for inching in setting up the strip before each pass, to furnish the power for initial tensioning of the strip before each pass and to furnish booster potential for speed control of the Winding reel motor and booster potential for the reel motor which is acting as a generator in providing regenerative braking for the unwinding reel during the rolling operation.

Another object of my invention is to provide, in a reversing strip mill system, a pair of booster generators of different capacities and a selective control system by which the boosters may be set up to operate so that, during the rolling operation, one of the boosters shall always be effective in the winding reel motor circuit and the other booster shall always be effective in the unwinding reel motor circuit, and a further control for using the boosters as they are set up by the first selective control for driving the reel motors for inching and initial tensioning operations.

Another object of my invention is to provide a booster generator in series circuit with each of the reel motors of a reversible strip mill so that the voltage applied to the winding reel motor may be greater than the power source voltage and the voltage generated by the reel motor which is acting as a generator in providing regenerative braking for the unwinding reel may be less than the voltage of the power source and to further provide means for varying the boostergenerator voltage in accordance with the variation of voltage of the power source.

A further object of my invention is to provide a booster generator in series circuit with the reel motor of a strip mill and a control system whereby the booster generator may be made-to supply power to the reel motor for providing initial tensioning of the strip before starting the mill and whereby the booster voltage may be increased when the mill is started to insure sufcient initial tensioning of the strip.

Another object of my invention is to provide a booster generator for each of the reel motors of a reversible strip mill and to so control the operation of the mill reel motors and boosters as to use the boosters to furnish power for initial tensioning of the strip before each pass and to furnish booster potential for speed and tensioning control of the winding reel motor and booster potential for the reel motor which is acting as a generator in providing regenerative braking for the winding reel during rolling operation, and to so control the booster generators as to cause an increase in their excitation as the rolling operation is started to insure sucient strip tension from the beginning of the rolling pass.

Other objects and advantages of my invention will become apparent from the following description of its structural and operating features and the accompanying drawings, in which:

Figures l and 2, when placed side by side show diagrammatically the essential parts of the sys` tem of my invention and their operative relationships; and

Figs. 3 and 4, when placed side by side, show diagrammatically a modication of the system of Figs. l and 2.

In practicing the invention, the roll driving motor is energized from a main generator and the speed and direction of rotation of this motor are governed by the main generator voltage as controlled by the value and polarity of its field excitation. Each reel motor is adapted to act as a generator to provide regenerative braking when its reel is the unwinding reel and in so operating feeds power back to the power source. rlhe reel motors are energized from the main generator. v

A booster-generator is provided for each reel motor and each has its armature connected in series with its reel motor armature. Each booster generator has a main eld winding which is connected to the main generator to automatically vary the booster voltage as the voltage impressed on the roll motor and reel motors is Varied. The booster generators also have auxiliary eld windings which are excited from a source of xed potential.

The reel -motor eld windings are controlled by regulators which are governed by the reel motor armature currents to maintain a constant tension on the material as it passes through the rolls.

Switching means are provided for connecting each reel motor with its booster generator and for governing the direction of rotation of the separate reel motors so that they may be individually controlled for rotation in either direction in setting up the strip in the mill before each rolling operation.

Control means are also provided for connecting the boosters and reel motors in series circuit relation so that the boosters energize the reel motors to establish the proper tension on the strip on each side of the roll before each pass of the strip through the roll. The booster generator auxiliary field excitation is increased While this initial tension is being established so that the reel motors may have sucient torque to provide the proper tension.

After the initial tension is established the main generator ileld winding is energized and the main field windings of the booster generators are energized in such a direction as to cause the voltage of the booster which is associated with the winding reel motor to add to the main generator voltage, thus impressing upon the winding reel motor a voltage higher than the main generator voltage. At the same time, the voltage of the other booster generator is in such a direction as to oppose the main generator voltage, thus allowing the unwinding reel motor, which is now acting as a generator to provide regenerative braking, to supply power to the main generator circuit while generating at a voltage less than the main generator voltage.

Because of the reduction in thickness of the strip material in passing through the mill, it is delivered from the mill much faster than it is fed to the mill. This necessitates running the winding reel faster than the unwinding reel. If the speeds of these reels were governed by the eld excitation of the reel motors, it would be necessary to provide an extremely large range of eld excitation to provide the relatively weak eld necessary for the high speed of the winding reel motor and the strong field necessary for the unwinding reel motor acting as a braking generator.

As the main'generator voltage is increased and the mill speed increased as a result of this voltage increase, the booster voltages increase because of increased excitation of their main eld windings,

thus impressing a voltage on the reel motor which will increase its sped without a change in its field excitation. At the same time, the increase of generated potential of 'the booster associated with the unwinding reel motor is increased and, since this voltage is in such a direction as to assist the unwinding reel motor generated voltage in bucking the voltage of the main generator, this increase will enable the unwinding reel motor to run faster while still furnishing no more than the necessary torque for maintaining the proper back tension on the strip.

In a modification of the system, booster generators of diiferent voltage and power capacities are employed with the booster generator of the larger capacity always acting in circuit with the unwinding reel motor and the booster generator of the smaller capacity always connected to the winding reel motor. In this system, set-up means is employed for connecting the boosters in the relation to the reel motors which they will have in the next rolling pass, then the set-up and tensioning functions are performed with the boosters as power sources as described hereinbefore.

Only such control devices as are necessary for causing the various motors and generators of this invention to perform the desired functions have been shown in this specification. Other control devices and systems will be readily suggested to one skilled in this art and many of such control devices which have been used in prior art devices, such as that disclosed in application Serial No. r105,073, filed January 3, 1934, now Patent No. 2,084,035, June 15, 1937, may be applied to the control of the system of the present invention without departing from the spirit of this invention.

Referring to. the diagram comprising Figs. 1

` and 2 of the drawings, I have shown -a mill roll stand 2 which is driven by a motor 3 to rollthe strip I.

Reels 4 and 5 are driven by motors 6 and 1 and act as winding or unwinding reels for the strip I depending upon the direction of pass of the strip through the mill. Motors 6 and 1 alternately act as motors and generators depending upon whether they are being used as motors to wind up a strip as it is delivered from the roll and to maintain tension on the strip in so doing, or as generators to furnish a load for the reel to maintain a back tension on the strip as it is unwound from the reel and fed to the rolls.

Power for driving the main roll motor 3 and reel motors 6 and 1 is furnished by a main generator 8 which is constantly driven by motor 23. Motor 23 also drives an exciter 9 which furnishes exciting current for the motors and generators in the system and also furnishes power for the control relays.

Booster generators I2 and I3 are provided and have their armatures connected in series circuit with the armatures of reel motors 6 and 1, respectively. These booster generators are also constantly driven by the motor 23.

A control switch generally designated at I4 is provided for selecting the direction of operation of the mill and reel motors.

Regulators I5 and I6 are provided for so controlling the fields of motors 6 and 1 as to maine tain a constant current in the motor circuits which in turn results in a c'onstanttension on the strip asy one motor is winding the strip and the other motor is serving as a back tensioning means for the strip as it unwinds.

Selector switches I1 and I 8 are provided for connecting the reel motors in circuit to be driven operate' independently4 of each other and in either direction.

The field winding 25 of mill motor 3 is energized from exciter 9 through resistance 24'which maybe varied to provide the desired excitation for this motor. This excitation is constant and always of the same polarity.

The direction of rotation of mill motor 3 is determined by the polarity of the main generator 8 which is controlled by, the excitation of its field winding 26 in a well known manner. Reversal of motor 3 is accomplished by reversing the excitation of the field winding 26 through the reversing switch which is a part of control switch I4 and which comprises movable contact elements 21 and 28 and fixed contact elements 29. Variation in speed of motor 3 is accomplished by varying the potential applied thereto from generator 8.` This variation of potential is accomplished by varying resistance 30 to vary the excitation of generator 8.

The regulators I5 and I6 operate to maintain a constant current in the armatures of motors 6 and 1 whether these motors are acting as driving motors or braking generators for the reels, by varying the field excitation of these motors. While these regulators may take any form which will accomplish the desired result, I have shown themin the form of a relay having front and back contact elements and a movable contact element which is spring biased to close the circuit through a back Contact element and is actuated by a coil to close a circuit through the front contact element. These parts are shown in regulator I5 as coil 3|, front contact element 32, back contact element 33, movable contact element 34 and biasing spring 35. Regulator I6 has corresponding parts. Coil 3l is energized by the drop across resistance 36 which is in series circuit relation with the armature of motor 6. When motor 6 is operating as a winding reel motor, its field winding 31 is normally excited through a circuit which includes one side II) of the excitation bus, conductor 38, resistance 39, conductor 40, field winding 31, conductor 4I and conductor 42 to the other side II of the excita tion bus. When the motor current exceeds the amount necessary to maintain the desired tension on the strip, Contact element 34 is moved by coil 3I to complete a circuit with'contact element 32. The circuit which is completed by contact elements 32 and 34 acts to short out the resistance 39 and comprises excitation bus I0, conductor 43, contact element 44, which has been moved to the left-hand position in selecting the direction of operation of the motors, conductor 45, contact elements 32 and 34 and conductor 46.

rI"his increase in the excitation of the motor results in decreased armature current which in turn decreases the tension exerted by the motor on the strip, and permits the biasing spring 35 to break the contact elements 32 and 34. operation is repeated as often as is necessary to maintain the armature current cons-tant.

When motor 6 is used as a braking generator to provide a back tension on the strip as it is being fed from reel 4 to the rolls, all of the contact elements of control switch I4 will be moved to the right-hand position and the contact ele- This ment 41 will complete a circuit for short circuiting the resistance 39, which circuit comprises excitation bus IU, conductor 43, Contact element 4'1, conductor 48, back contact element 33, contact element 34 and conductor 46. When the current in the armature circuit of machine 6 decreases to where it no longer furnishes suicient back tension for the strip when machine 6 is acting as a generator for regenerative braking, the coil 3l allows movable' contact element 34 to engage contact element 33 to complete the short circuit for resistance 39 and to thus increase the excitation of machine 6. This increase in excitation will cause the machine 6 to pick up more load, thus increasing its back tension on the strip and also its armature current. This operation is repeated under control of the armature current of machine 6 as often as isl necessary to maintain the armature current constant.

The operation of regulator I8 to control the armature current of machine I, both when it is operating as a motor and as a generator to provide regenerative braking, is the same as that of regulator I5 in connection with machine 6, and regulator I6 is so connected with control switch I4 as to cause its back contact elements to be in circuit when the front contact elements of regulator I5 are in circuit.

When machine 6 is operating as a motor to drive reel 4 to tension the strip as it winds on reel 4, booster generator I2 is so excited as to generate a voltage which will add to the voltage impressed upon motor G by generator 8 and will thus operate motor 6 at a voltage above the main generator voltage. This booster voltage is useful in providing suiicient voltage for motor 6 to cause it to maintain a constant tension on the strip when the mill motor is just starting up and the Voltage of generator 8 is very low.

Booster generator I2 is provided with an auxiliary eld winding 49 and a main field winding 2|. The auxiliary field winding is excited from the excitation bus.- The main field is excited from the main generator 8 and always has a strength which is proportional to the voltage of the generator 8.

When machine 6 is acting as a braking generator for the reel 4, it is necessary that the excitation of booster generator I2 be of the same polarity as it was when machine G was acting as a motor so that its generated voltage will buck the voltage applied to machine 5 by generator 8 and will thus decrease the voltage which it is necessary for machine 6 to generate in order to feed power back to generator 8. To accomplish this, it is necessary that the main field winding 2I of booster generator I2 be reversed, since the polarity of the voltage of generator 8 has been reversed under these conditions to reverse the direction of the operation of the mill.

Reversing switch 2D is provided for the purpose of reversing the polarity of main eld winding 2| of booster generator I2 as above described. The operation of reversing switch 2G is controlled by control switch I4 through its contactor elements 50 and 5I and relay coils 52 and 53.

The control of booster generator I3, which is connected in series with machine I, is the same as that hereinbefore described for machine 6 and booster generator I2. This control will -be obvious from an inspection of the circuits to the corresponding elements of the two devices.

When the strip of material to be rolled is being set up in the mill preparatory to the actual rolling operation, it is handled by motors 6, and I to feed it to the mill and to place it in the proper position. For this operation, it is necessary that motors 6 and 'I be separately controllable to operate in either direction. This operation is known as the inching operation.

The inching operations are accomplished by furnishing power to the motors 6 and I from their respective booster generators I2 and I3 under control of switches I'I and I8. In the control of motor 6, the circuit through the motor from`the booster isl completed by contact elements 54 of selector switch I'I which causes relay -55 to operate. Upon the operation of relay 55, its contact element 5S closes a series circuit which includes motor 6, resistance 36, conductor 5I, booster generator I2, conductors 94, 58, 5B and 60, contact element 58 and conductors 6I and 62 to the armature of motor 6.

-At the same time, the auxiliary eld winding 49 of booster generator I2 is energized by the selector switch I'I in such a direction as to cause booster generator I2 to furnish a potential to motor 6 of a polarity which will cause it to rotate in a desired direction. Switch I'I is a selector switch in that it has reversing contacts which will cause energization of the field winding 49 in the desired selected direction.

The operation of selector switch I8 is similar to that of switch I'I and it functions to connect booster generator I3 in series circuit with motor 'I and to select the direction of operation of motor 'I by selecting the direction of energization of the auxiliary field winding 63 of booster generator I3.

After the inching operations have been performed, the strip is set up in the mill and ready to be rolled. Before initiating the rolling operation, it is necessary that the tensions which are to be maintained on the strip on both sides of the roll, while the mill is running, be established. This tensioning is accomplished by circuits which are under control of the control switch I4 and is accomplished by connecting booster generators I2 and I3 and motors 6 and I in a series circuit and so exciting the booster generators as to cause them to generate voltages in the same direction in the series circuit. This causes motors 6 and 'I to tend to run in opposite directions and thus tension the material on each side of the rolls. This series circuit is established by moving control switch I4 to its first position to close a circuit which includes excitation bus I0, conductor 54, relay coil 65, conductor 66, contact element 6I or 68 depending on the direction of movement of the control switch I4, and conductor 69 to the other excitation bus II. This energization of relay coil 65 causes closure of its contact element I0 completing a series circuit which includes motor 6, resistance element 3S, conductor 5'I, booster generator I2, conductor 53, booster generator I3, conductor 'II, resistance "I2, motor 1, conductor I3, contact element "IIJ, conductors 14 and 62 to the other side of motor 8. This circuit is also maintained by control switch I4 throughout the rolling pass.

At the time the control switch I4 is moved to its first position to cause the connection of the booster generators and motors in the tensioning circuit, a circuit is closed to energize the auxiliary eld windings 49 and 63 of booster generators I2 and I3 applying less than `full potential from the excitation bus to these elds. This reduced excitation is necessary to prevent the application of such a high excitation potential to the reel motors while they are at standstill as would damage the commutators and brushes because of excessive amature current. The energizing circuit thus established for eld winding 49 extends from excitation bus II, through contact element 15 or contact element 16, conductors 11 and 18, auxiliary eld 49, conductors 19 and 88, contact element 8I or contact element 82, conductor 85, resistance I9 and conductor 83 to the other excitation bus I0. l

When the rolling operation is started by applying potential to the mill motor 3, it is desirable that the strip tension is increased to insure sufficient tension on the strip to produce the proper reduction in thickness of the beginning end of the strip. To this end full field excitation of the booster generators is produced by shorting out the resistance I9 on the second step of the control switch I4. When the control switch I4 is in the running position, which is the second step oi the switch, the circuit for the auxiliary eld winding 49 of booster generator I2 extends from excitation bus II, through contact 15 or contact 16, conductors 11 and 18, iield winding 49, conductors 19 and 80, contact element 8| or contact element 82 and conductor 83 to the other side of the excitation bus I0.

The control of the auxiliary winding 63 of booster generator I3 is effected in a similar manner by control switch I4 through the corresponding circuits which will be obvious from an inspection of the drawings.

When the control switch I4 is moved to its second position, a circuit is completed to connect the two series circuits, comprising booster generator I2 and machine 6 and booster generator I3 and machine 1, in parallel across the.main generator 8.- 'I'his is accomplished by the lower section of contact elements 61 or 68 which close an operating circuit for relays 86 and 81. The operation of relays 86 and 81 causes theclosure of contact elements 88 and 89 and completes the connection of the armatures of the motors and booster generators with the main generator.

The circuit thus established through machine 6 comprises main generator 8,` conductor 9U,

` circuit breaker 9I, conductors 92 and 93, contact element 88, conductors 58 and 94, booster generator I2, conductor 51, resistance 36, machine 6, conductors 62 and 95, contact element 89 and conductors 96 and 91 to the other side of the main generator 8.

The circuit which is established through machine 1 comprises main generator 8, conductor 90, circuit breaker 9I, conductors 92 and 93, contact element 88, conductor 58, booster generator I3, conductor 1I, resistance 12, machine 1,v conductor 13, contact element 10 which was energized when the control switch I4 was moved to its first position, conductors 14 and 95, contact element 89 and conductors 96 and 91 to the other side of main generator 8.

At the time that the relay 65 was energized by control switch I4 to establish a tensioning circuit for the reel motors 6 and 1 and booster generators I2 an-d I3, relay coil 98 which is connected in parallel with relay coil 65, was energized to close contact element 99 establishing an energizing circuit for main motor 3 which includes main generator 6, conductor 90, circuit breaker 9| conductor 92, motor 3, conductor |88, Contact element 99 and conductor 91 to the other side of the generator`8.

summarizing, the steps in the operation ofthe Whole system are as follows: The strip y'I is set up in the mill by operation of selector switches I1 and I8 to the left or right depending upon the direction of rotation desired for motors 6 and 1. After the set up operation is accomplished, selector switch I4 is moved one step to the right or left, depending upon the desired direction of operation of the mill. This rst step energizes the auxiliary booster generator eld winding and connects the booster generator armatures and'motor armature in series to establish a forward and back tension on the strip. After the tensioning is established, selector switch I4 is moved to the second position which causes the motors 6 and 1 with their associated booster generators I2 and I3 to be connected in circuit with the main generator 8.

At the same time, the iield winding of main generator 8 is connected to the excitation bus in such a manner as to cause the generator to generatea voltage of the desired polarity to cause the mill to run in the proper direction for the operation whichy is just started. On this second step the current regulators I5 and I6 are also connected to so govern the current in the armatures of reel'motors 6 and 1 as to cause them to maintain the proper tension on the strip during the rolling operation. The mill is now brought up to the running speed by a variation of resistance 30 to increase the excitation of the main generator and thus increase the voltage applied to the motor system.

The operation of control switch I4 to its second step also causes contact element 5U or 5I, depending upon the direction of operation of the mill, to cause relay 52 or relay 53 to so control the switching device 20 as to energize the main eld windings 2| and 22 of the boosters in such l a direction as to secure proper polarity of booster voltage and, since these elds are now connected to the main generator bus they will cause the booster voltage to varywith the mill motor speed to thus vary the potential applied to the reel motors in the proper proportions to maintain the strip tension at all times.

Figs. 3 and 4, taken together, form a wiring diagram for a modification of the system shown in Figs. 1 and 2, in which booster generators of different Voltage capacities are provided. In this system connections are provided for causing the boost' generator of the smaller voltage capacity to be connected in circuit with the reel motor which has been selected to function as the winding reel motor in the operation of the mill. Likewise, the booster generator of the 'larger voltage'capacity is connected in circuit with the reel machine which has been selected to operate as the regenerative brake in the operation of the mill.

While, under the particular conditions of the apparatus herein described, it is most desirable to have the booster of the smaller voltage capacity always acting in the circuit of the reel motor which is serving as a driving motor for winding reel and the booster generator of the larger voltage capacity acting in the circuit of the reel motor which isacting as the regenerative brake for the unwinding reel, I do not wish to be limited to this specific method of using the booster generators since vsome conditions of operation might arise that would make the use of the booster generator of larger voltage capacity with the winding reel motor and the booster generator of the smaller voltage capacity with the machine acting las a regenerative brake desirable. The important difference between this system and the system hereinbefore described in connection with Figs. 1 and 2 is that this system always uses the same booster generator with whatever machine is acting as a reel motor and always uses the same booster generator with whatever machine is acting as a regenerative brake.

Except for the changes necessary in connecting these booster generators in their proper circuits, the operation of the system of Figs. 3 and 4 is the same as that of the system shown in Figs. 1 and 2. Like reference characters denote the corresponding elements of apparatus on the two diagrams.

Since the connection of the two booster generators is to be changed each time the mill is reversed, it is necessary that the reversing switch for the auxiliary eld windings of the booster generators be provided in order to cause the generators to generate a voltage of the proper polarity while the mill is operating. To accomplish this, selector switch |0| is provided as a set up switch to provide the proper connections for booster-generators |02 and |03 for the next rolling operation of the mill. When it is desired to make a rolling pass from right to left, selector switch |0| is moved from right to left to energize relay coils |04 and |05, causing the Contact elements |08 and |09 ofv these relays to establish the proper connections to cause booster generator |03 to be connected in series circuit with reel motor and booster generator |02 to be connected in series circuit with reel motor '5, and also to so connect the auxiliary eld windings |06 and |0ll of booster generators 02 and |03 as to establish the proper polarity of booster generators |02 and |03 to cause these booster generators to generate voltages in the proper directions during the next rolling operation.

When the mill is to be operated in the opposite direction, selector switch |0| is moved to the other position causing control relays |0 and to reverse the positions of the booster generators through their contacts ||2 and 3. Energization of relays |04 and |05 or ||0 and also causes reversing switches I4 and ||5 to establish the proper connections for the auxiliary eld windings |06 and |01 for the booster generators.

Since the booster generator |03 is always to serve as the winding reel motor booster and booster generator 02 is always to serve as the unwinding reel machine booster, it is necessary,

when the connections `on these machines4 are re.

versed by the selector switch |0|, to reverse the connections from set up switches l1 and i8 to the booster auxiliary field windings so that switch may always control the machine B and switch l0 will always control machine 'I regardless of which booster is being used with these machines. This is done by connecting selector switches I|6 and l l'l in the booster iield circuits from the control switches |7 and lB and actuating these switches ||6 and by relays |04 and respectively, as these relays are selectively energized by connection through selector switch |0|.

With these connections established set up switches il and |8 are used to control the operation of motors 6 and l and their associated booster generators |02 and |03 to accomplish the necessary set up operations for the mill as hereinbefore described.

After these set up operations are accomplished, the strip is placed under tension as hereinbefore described by moving control switch |4 t0 its rst step to the left. This establishes the tensioning circuits as hereinbefore described.

The mill is then put into operation by moving control switch I4 to its second step to the left and Varying the resistance 30 to bring the mill up to speed. All of the other elements and connections for operation of the elements are the same as was described in. detail in connection with Figs. 1 and 2. A change has been made, however, in the wiring diagram in that relay coil 65 in the diagram comprising Figs. 3 and 4 has been made to accomplish the function of both relay coil 65 and relay coil 98 of the diagram comprising Figs. 1 and 2 and the relay coil 86 of the diagram comprising Figs. 3 and 4 has been made to establish the connections made by relays 86 and 81 in the diagram of Figs. 1 and 2. This does not affect the operation of the system, but merely tends to simplify the wiring diagram,

The circuit breaker 9| is not an essential part of the invention, but may be the usual protective circuit breaker which is used in such circuits. The various resistances, such as the eld resistance ||8 in the field circuit of the exciting generator, resistance 24 in the field circuit of the main motor, resistance 39 in the field circuit of the motor 6 and also the resistance 22 in the eld circuit of reel motor 'l and the resistance i9 and resistances 36 and "l2, may be varied to establish the correct adjustment for the proper operation of the system.

It will be seen that I have provided a reversing strip mill with means for extending the speed range of the reel motors of the mill which alternately act as winding reel motors and as unwinding reel braking generators without the necessity of extreme variations in field control of these motors by providing a booster generator for each of these reel motors and that I have further provided for utilizing these booster generators to furnish the power for the reel motors with which they are associated in setting up and tensioning the strip material in the mill preliminary to the rolling operation.

In compliance with the requirements of the patent statutes, I have shown and described herein the preferred embodiments of my invention.

.. It is understood, however, that the invention is not limited to the precise construction shown and described, but is capable of modification by one skilled in the art, the embodiments herein shown being merely illustrative of the principles of my invention.

I claim as my invention:

1. In a rolling mill, winding and unwinding reels for handling strip material being worked by the mill, dynamo-electric machines for driving the reels, a power source, booster generators, and means whereby either of said dynamo-electric machines may be connected to the power source as a motor in series with a booster generator and the other connected to the power source in series with a booster generator to operate as a braking generator to tension the material as it is being fed to the mill.

2. The combination with a mill for rolling strip material having winding reels disposed on opposite sides thereof for winding up andY unwinding the strip, of a motor for driving the rolling mill, a source of power, a motor for driving one of said reels to wind up the strip, a booster generator having an armature connected in serieswith the motor armature for boosting. the motor driving potential above the potential of the source of power, a braking generator having driving connection with the other reel for exerting tension on the unwinding strip and a booster generator having an armature connected in series with the braking generator armature for causing the braking generator to return energy to the power source regardless of its speed of operation.

3. In combination, a roll stand for working strip material, winding reels on opposite sides thereof for handling the material, a source of power, means for driving the roll stand at different speeds, dynamo-electric machines connected to the reels adapted to alternately function as motors receiving power from the power source and as braking generators returning power to the power source dependent upon the direction of operation of the roll stand, a booster generator connected in series with each of the dyname-electric machines, means for causing each booster generator to generatey a voltage of such polarity as to a'dd to or oppose the power source voltage depending upon whether its associated dynamo-electric machine is acting as a motor or a generator, and regulator means associated with each dynamo-electric machine for maintaining its load current substantially constant at a predetermined valuethereby to subject the material to asubstantially constant tension regardless of the speed of the roll stand.

4. In a rolling mill, winding and unwinding reels for handling the material being worked by the mill, a source of power, a roll stand, means for driving the roll stand at different speeds, dynamo-electric machines connected to the reels adapted to alternately function as motors receiving power from the power source and as braking generators returning power to the power source depending upon the direction of operation of the roll stand, a booster generatorconnected in series with each of the dynamo-electric machines, means for causing each booster generator to generate a volt-age of such polarity as to add to or oppose the power source voltage depending upon whether its associated dynamo-electric machine is acting as a motor or a generator, means for varying the voltage generated by the booster generators proportionately with the variation in roll stand speed, and regulator means associated with each dynamo-electric machine for maintaining its load current substantially constant at a predetermined value thereby to subject the materialto a substantially constant tension regardless of the speed of the roll stand.

5. In combination, a Work device, a motor for driving the work device, a reel for holding material to be worked by the work device, a reel for receiving the material as it is worked by the Work device, a dynamo-electric machine connected in.

driving relation to each of the reels, the dynamoelectric machine associated with the receiving reel to be driven as a motor, theother dynamoelectric machine disposed to be driven by the reel as a regenerative brake to tension the material as it is unwound by the work device, means for varying the voltage of the power source to vary the speed of the work device, a booster generator connected in series circuit relation with each dynamo-electric machine to the power source, the booster generator associated ,with the receiving reel dynamo-electric machine being disposed' to generate a voltage of a polarity the same as the polarity of the power source and the booster generator associated with the regenerative dynamoelectric machine beingy disposed to generate a voltage of a polarity opposite to that of the power source, whereby the regenerative dynamo-electric Adriving the work device, a reel for holding and unwinding material to be worked by the work device, a reel for winding material delivered by the work device, a generator disposed to function as a brake for the unwinding reel to subject the material to tension, a motor disposed to drive the winding reel and to subject the material to tension, a source of variable voltage power for controlling the speed of the work device, a boostergenerator connected in Vseries with the braking generator across the variable voltage power source in such manner that the voltage of the boostergenerator and the braking generator are additive, a booster generator connected in series with the winding reel motor in such manner that its voltage and the power source voltage are additive, said booster generators being disposed to develop a voltage proportional to the voltage of the power supply, and regulator means operable to maintain the load currents of the braking generator and the winding reel motor substantially constant, whereby the braking generator may return energy to the power source while developing a voltage of lower value than that of the power source, and whereby constant tensions on the material are maintained by both the winding and unwinding reels regardless of the speed of the work device or diameter of the reel.

7. A control system for apparatus having an element operating on a strip of material comprising a pair of dynamo-electric machines connected to the strip, a supply source, circuit connections between said source and said machines, means for introducing a separate additional voltage into the circuit of each of said machines, and means controlling said voltages in accordance with the operation of said element.

8. A motor control system comprising in combination, a main motor for driving a load, a pair of dynamo-electric machines connectedto said load, a source of supply, separate circuit connections from said source to said motor and each of said dynamo-electric machines, a generator in series circuit relation witheach of said dynamoelectric machines, means for controlling the direction of rotation of said motor and for effecting operation of one of said machines as a generator and the other as a motor when said main motor is rotating in one direction and for reversing the operations of said machine when said motor is rotating in the opposite direction.

9. A control system for strip mills and the like in which the gauge of the strip is reduced by mill rolls situated between a winding up reel and an unwinding reel comprising a motor for driving said rolls, separate dynamo-electric machines connected to said reels, vmeans for supplying voltage to said motor and to said machines, and means for extending the operating range of said dynamoelectric machines beyond that obtainable with eld control comprising means for introducing into the circuit of `said unwinding reel dynamoelectric machine a voltage having a polarity additive to the voltage of said machine, means for introducing intr the circuit of said winding reel dynamo-electric machine a voltage having a polarity additive to the source voltage to compensate for the difference in the speeds of said dynamo-electric machinesdue toreduction in` gauge of the strip. l

10. In a reversin'g strip mill having a roll stand 'IISl and a reel in either side of the stand to feed the strip to and receive the strip from the rolls, the combination of a dynamo-electric machine associated with each of the reels to drive or be driven by the reel depending upon the direction of pass of the strip through the rolls, a booster generator connected in circuit with each of said dynamoelectric machines, means for so controlling the booster generators as to cause the voltage of the generator associated with the machine that is acting as a reel motor to be added to the motor driving voltage and the voltage of the generator associated with the machine that is being driven by the reel to add to the voltage generated by said machine while the mill is operating, and control means for operating each of the dynamo-electric machines as a motor from its associated booster generator in performing the necessary operations in handling the strip in setting up the strip in the mill preliminary to each rolling operation.

11. In a strip mill having a roll stand, Winding and unwinding reels for the strip, a motor for driving the winding reel and a dynamo-electric machine acting as a regenerative brake for the unwinding reel, the combination of a generator connected in series with the motor having the same polarity as the motor driving source and a generator connected in series with the regenerative braking machine having the same polarity as the braking machine.

12. In a strip mill having a roll stand, winding and unwinding reels for the strip, a motor for driving the winding reel and a dynamo-electric machine acting as a regenerative brake for the unwinding reel, the combination of a generator connected in series with the motor having the same polarity as the motor driving source and a generator connected in series with the regenerative braking machine having the same polarity as the braking machine, and control means for causing the motor and the dynamo-electric machine to be driven from their associated generators in performing the necessary operations in handling the strip in setting up the strip in the mill preliminary to each rolling operation.

13. In a strip mill having a roll stand, winding and unwinding reels for the strip, a motor for driving the Winding reel and a dynamo-electric machine acting as a regenerative brake for the unwinding reel, the combination of a generator connected in series with the motor having the same polarity as the motor driving source and a generator connected in series circuit with the regenerative braking machine having the same polarity as the braking machine, control means for causing the motor and the dynamo-electric machine to be driven from their associated generators in performing the necessary operations in handling the strip in setting up the strip in the mill preliminary to each rolling operation, and

control means for causing the two generators to so energize the motor and dynamo-electric machine as to establish forward and back tensions on the strip after it is set up in the mill preliminary to the rolling pass through the mill.

14. A motor control system comprising in combination, a main motor for driving a load, a pair of dynamo-electric machines connected to said load, a source of supply, separate circuit connections from said source to said motor and each of said dynamo-electric machines, means for controlling the direction of rotation of said main motor and for effecting operation of one of said machines as a generator and the other as a motor when said main motor is rotating in one direction and for reversing the operations of said machines when said main motor is rotating in the opposite direction, a pair of booster generators and control means for causing a predetermined one of said booster generators to always be connected in circuit with the machine which is acting as a motor and the other generator to always be connected in circuit with the other machine.

l5. A control system for apparatus operating on a strip of material comprising a pair of dynamo-electric machines mechanically connected to the strip, a source of variable voltage, circuit connections from said source to said machines, and means for introducing into the circuit of said source and each of said machines a voltage proportional to the voltage of said source, the said voltages being dinerent in value.

16. In a rolling mill or the like having an element for reducing the thickness of a strip of material and having Winding and unwinding reels, a control system comprising a motor for driving said element, a pair of dynamo-electric machines, one connected to each of said reels, supply means for said motor and dynamo-electric machines, and means for extending the speed range of the dynamo-electric machines beyond that obtainable with field control comprising a pair of generators of different voltage ratings and control means for causing the generator having the lower voltage rating to be so connected in the circuit of the Winding reel dynamoelectric machine that its voltage will add to the voltage of the supply source and for causing the other generator to be so connected in the circuit of the unwinding reel dynamo-electric machine that its voltage will add to the voltage generated by said machine.

1'7. In a reversing strip mill having a roll stand and a reel on either side of the stand to feed the strip and to receive the strip from the rolls, the combination of a dynamo-electric machine associated with each of the reels to drive or be driven by the reel depending upon the direction of pass of the strip through the rolls, a pair of booster generators having diierent voltage ratings, means for so controlling the booster generators as to cause the one having the lower voltage rating to be so connected in circuit with the machine that is acting as a reel motor as to cause its voltage to add to the motor driving voltage and to cause the other booster generator to be so connected in circuit with the machine that is being driven by the reel as to cause its voltage to add to the voltage generated by said machine while the mill is operating, and control means for operating each of the dynamo-electric machines as a motor from either of the booster generators in performing the necessary operations in handling the strip in setting up the strip in the mill preliminary to each rolling pass, and control means whereby the dynamo-electric machines are connected in circuit with the booster generators in the relation which they will have during the next rolling pass, so that the dynamoelectric machines may be driven by the booster generators to tension the strip after it is set up in the mill and preparatory to the next rolling pass.

l 18.In a strip mill having a roll stand, winding and unwinding reels for the strip, a motor for driving the Winding reel and a dynamo-electric machine acting as a regenerative brake for the unwinding reel, the combination of a generator connected in series with the motor having the is unwound from the reel by the work device,

same polarity as the motor driving source and a generator connected in series circuit with the regenerative braking machine having the same polarity as the braking machine, and control means for causing the two generators to so energize the motor and dynamo-electric machine as to establish forward and back tensions on the strip after it is set up in the mill preliminary to the rolling pass through the mill.

19. A control system for strip rolling mill apparatus having a pair of main rolls and winding and unwinding reels comprising, in combination, a pair of dynamoeelectric machines one connected to each of said reels, a source of supply for said dynamo-electric machines, control means providing operation of the unwinding reel machine as a generator and the winding reel machine as a motor, a means for extending the operating range of said machines beyond that obtainable with field excitation comprising a generator for each of the machines having their armatures connected in circuit with each of the machines, each generator provided with a`main field winding energized in accordance with the speed of the strip, the generators being so disposed' that the voltage of the generator associated with the winding reel machine is of the same polarity as that of the power source and the voltage of the generator associated with the unwinding reel machine is the same as that of the unwinding reel machine, and an auxiliary field'l winding on each of said generators, means for so connecting said booster-generators and their associated dynamo-electric machines as to perform the necessary operations in handling the strip in setting up the strip in the mill preliminary to each rolling pass, means for so connecting said booster generators and dynamo-electric machines as to establish forward and back tension on the strip preliminary to the rolling pass through the mill, and means for causing the auxiliary fields to have less strength during the tensioning operations than during the rolling operation.

20. 'Ihe combination with a rolling mill and winding and unwinding strip handling reels located on opposite sides thereof, of a dynamoelectric machine connected to each reel disposed to function as a driving motor or a regenerative brake therefor, a source of power, a booster gene erator connected, in series circuit relation with the dynamo-electric machine which serves as the driving'motor, to the power source yin such a manner that the power source voltage and the booster generator voltage are added, and a booster generator connected, in series circuit rela tion with the dynamo-electric machine which serves as the regenerative brake, tothe power source in such a manner that the voltages of the booster generator vand regenerative braking dynamo-electric machine are added, whereby said braking dynamo-electric machine may regenerate power without developing a voltage as high as that ci the source.

21. In combination, a work device, a power source, a motor for driving the work device connected to the power source, a reel for holding material to be worked by the work device, a reel for receiving the material as it is worked by the work device, a dynamo-electric machine connected to each of the ree1s,vthe dynamo-electric machine associated with the receiving reel to be driven as a motor, the other dynamo-electric machine disposed to be driven by th'e reel as a regenerative brake to tension the material as it means for varying the voltage of the power source to vary the speed of the work device, a booster generator connected in series circuit relation with each dynamo-electric machine to the power source, the booster generator associated with the receiving reel dynamo-electric machine being disposed to generate a voltage of a polarity the same as the polarity ofthe power source and ,the booster generator associated with the regenerative dynamo-electric machinev being dison a strip of material comprising a pair of dynamo-electric machines mechanically connected to the strip, a source of variable voltage, circuit connections from said source to said machines, and means for introducing into the circuit of each of said machines a separate auxiliary voltage proportional to the voltage of said source.

23'. A control system for strip rolling mill apparatus having a pair of main rolls andl winding and unwinding reels comprising in combination, a pair of dynamo-electric machines, one connected to each of said reels, a source of supply for said dynamo-electric machines, control means providing operation of the unwinding reel machine as a generator and the winding reel machine as a motor, a means for extending the operating range of said machines beyond that ob tainable with field excitation comprising a generator for each of the machines having their armatures connected in circuit with their associated machines, each generator provided with a main iield winding energized in accordance with the speed of the strip, the generators being so disposed that the voltage of the generator associated with the winding reel machine is of the same polarity as that of the power source and the voltage of the generator associated with the unwinding reel machine is the same as that generated by the unwinding reel machine, and an auxiliary iield winding on each of said generators .excited for energizing said unwinding reel machines to exert a tension on the strip when the mill is stalled.

24. The combination with a roll stand and winding reels, positioned on opposite sides of the roll stand for subjecting the material being rolled to tension on both sides of the roll stand, motors for driving the reels, a generator for supplying power to said motors, a pair of booster generators, means for connecting the roll stand motor to the power source, meansl for connecting each of the reel motors in series with one of the booster generators to the power source, and means including a regulator foreach reel motor for controlling the excitation of the reel motors to maintain predetermined tensions on the-material passing through the mill stand.

25. In combination, a stand of reducing rolls, a main motor for driving the reducing rolls, winding reels on opposite 'sides of the roll stand for passing strip material back and forth through the roll stand, dynamo-electric machines connected to the reels, a source ot' power, means operable to alternately connect the machines so that one will act as a motor to drive the winding reel and the other will be connected to be driven by the unwinding reel as a back tension generator to maintain tension on the strip as it passes back and forth through the reducing rolls, a pair of booster generators, means for so connecting the booster generators in series circuit relation with the dynamo-electric machines as to cause the voltage of the booster generator which is associated with the machine which is acting as a motor to add to the voltage of the source of power and the voltage of the booster generator which is associated with the machine which is acting as a back tension generator to add to the voltage of that machine, and means including a current regulator associated with each dynamo-electric machine operable to regulate the excitation of said machines to maintain al substantially constant tension on the strip material as it passes back and forth through the roll stand.

26. In a motor control system, in combination, a main motor for driving a load, a pair of dynamo-electric machines connected to sa-id load, a source of supply, separate circuit connections from said source to said motor and each of said dynamo-electric machines, means for controlling the direction of rotation of said motor and for eiecting operation of one of said machines as a generator and the other as a motor when said main motor is rotating in one direction and for reversing the operations of said machines when said main motor is rotating in the opposite direction, a pair of booster generators of different voltage ratings and control means for causing a predetermined one of said generators to always be connected in circuit with the machine that is acting as a motor and the other generator to always be connected in circuit with the other machine. v

27. A control system for apparatus having an element operating on a strip of material comprising a pair of dynamo-electric machines connected to the strip, a supply source, circuit connections between said source and said machines, means for introducing an additional voltage into the circuit of each of said machines and said source, one of said voltages being greater than the other, and means controlling said voltages in accordance with the operation of said element.

28. A control system for apparatus operating on a. strip of material comprising a pair of dynamo-electric machines mechanically connected to the strip, a source of variable voltage, circuit connections from said source to said machines, and means for introducing into the circuit of said source and each of said machines an auxiliary voltage proportional to the voltage of said source, said auxiliary voltages being different in value.

29. In areversing strip mill having a roll stand and a reel on either side of the stand to feed the strip to and receive the strip from the rolls, the combination of a dynamo-electric machine associated with each of the reels to drive or be driven by the reel depending upon the direction of pass of the strip through the rolls, a pair of booster generators having different voltage ratings, means for so controlling the booster generators as to cause the one having the lower voltage rating to be so connected in circuit with the machine that is acting as a reel motor as to cause its voltage to add to the motor driving voltage and to cause the other booster generator to be so connected in circuit with the machine that is being driven by the reel as to cause its voltage to add to the voltage generated by said machine while the mill is operating, and control means for operating each of the dynamo-electric machines as a motor from either of the booster generators in performing the necessary operations in handling the strip in setting up the strip in the mill preliminary to each rolling pass.

ALONZO F. KENYON. 

